The present invention relates generally to an optical media or material capable of transmitting an optical signal and, more specifically, to such a material and a method of making a material which is hydroxyl ion (OH) and hydrogen (H) resistant.
Silicon dioxide glass or silica is one form of glass used in optical fibers because of its clarity. Other optical materials including silicon have been used. Silicon based fiber has transmission losses. These transmission losses have three components: OH absorption, Rayleigh scattering and the Urbach tail.
Silicon based material is a hydrophilic material, which absorbs OH. This absorption produces transmission losses. The transmission losses in general are shown as graph 10 in FIG. 1 from Ref. 1. That is a graph of transmission losses as a function of wavelength. OH absorption produces the peak at approximately 1400 nanometers, which is approximately one-half of the fundamental OH mode. The Rayleigh scattering effect is illustrated by curve 12. Rayleigh scattering is proportional to 1/λ4. Thus, the Rayleigh scattering is wavelength or λ dependent. The scattering comes from the non-uniformities in the glass, which is disordered by its nature, even though the purity and homogeneity are carefully controlled during manufacturing. Light will scatter from any point where the refractive index varies. The Urbach contribution, as illustrated, produces the Urbach tail 14 beginning at approximately 1,600 nanometers. This results from the vibration of the silicon-oxygen (S—O) bond. The solid line 16 running across the bottom represents the sum of the Rayleigh and Urbach contributions, which may be the clarity limit in the silicon based glass.
Spatial spreading of light along the path of propagation is known as dispersion. Appropriate doping can be used to control dispersion. The dopant changes the index of refraction of the fiber by raising the index refraction. Confinement process is similar to internal refraction. Which dopant to use and how it is added is used to optimize all of the parameters associated with high capacity optical transmission systems. The particular configuration will determine the optimization of the interplay between dispersion and non-linearity.
The dependence of the loss mechanism on spectral wavelengths of silica standard (single) mode fibers SMF is illustrated in FIG. 2A. A comparison of the modal dispersion of transmitted signals in multimode and single-mode fibers is illustrated in FIG. 2B. See Ref 2.
Historically, optical systems have been designed around these limitations of the optical fiber by applying certain modifications and optimizations such as such as dispersion compensators, in-line amplifiers, etc. So, to reduce the transmission loss of fibers, various schemes have been used. These include cladding the basic fiber. Refs. 3 and 4 show two of the latest treatments to reduce intrinsic fiber loss.
Ref. 5 and Ref. 6 were one of the earliest attempts in doping silicon to produce a relatively high transmittance optical filter at desired wavelengths with relatively inexpensive cost, but still susceptible to water, as it is the case in the previous two Refs. Ref. 6 is the process used in Ref 5. Si and Te were heated at 1075° C. for 72 hours. The resulting structure of SiTe2 had to be kept in a vacuum to prevent decomposition in the atmosphere through the interaction with water vapor. These are either costly in material cost, and or as well in the cost of manufacturing. More recent analysis is presented in Ref 7.
The present invention is a method of forming a single crystalline structure having a substantially linear response at least over the wave lengths of 1,200 to 1,700 nanometers, the resulting structure and its use as an optical media. Thus, maximum obtainable transmission with zero attenuation is provided. There is no intrinsic material absorption.
For silicon base materials, the method produces a hydroxyl ion (OH) resistant silicon material. The transmission versus wavelength response is flat with no absorption peaks between 1,000 nanometers to the Urbach tail at 2,000 nanometers, at a minimum. There is no second harmonic of the hydroxyl ion vibration peak at 1,400 nanometers. The Rayleigh scattering has been substantially eliminated.
An example of a silicon based material produced by the present method is a silica-tellurium single crystalline structure. The structure is SiO2Tex where x is in the range of ⅓ to 5/3. The silica and tellurium structure includes twin crystal structures. The twining angle is 90 degrees. The method also includes silicon-tellurium single crystalline structures.
One method of the invention includes inserting two substances into a crucible and sealing the crucible in an envelope. The two substances are in an oven at a temperature and time sufficient to create a single crystalline material of the two substances having a substantially linear response at least over the wave lengths of 1,200 to 1,700 nanometers.
Another method includes inserting the two substances into a substantially spherical crucible. The crucible is sealed in a substantially spherical envelope. The two substances are heated in an oven at a temperature and time sufficient to create a single crystalline material of the two substances. Heating is carried out for a sufficient amount of time that all of the inserted material is converted to a single crystalline material of the two substances. The opening in the crucible should be large enough to receive the substances while maintaining the crucible spherical. For example, the diameter of the crucible is at least twice the diameter of an opening of the crucible through which the substances are inserted.
The resulting material of both methods are an aggregate of single crystalline material. The resulting material of either product may then be processed into an optical media. The material may also be used as a protective coating on metal or ceramics. This may be a crystal, wafer, rod or a fiber. No cladding or other treatment is necessary to obtain the transmission characteristics briefly described.
These and other aspects of the present invention will become apparent from the following detailed description of the invention, when considered in conjunction with accompanying drawings.